Hello,
My server instance is on Ubuntu 14.04 and this problem happens regardless of client OS ( I have tried the client on Archlinux and Windows 7).
I am successfully able to connect to my x2go server using the "Single Application" Session Type and I don't have any issues with it at all.
If I choose LXDE, KDE, or MATE as my Session Type, then the desktop displays properly, and as I hover my cursor over different icons, they highlight and then return to normal as the cursor moves on.
However, in any of these desktop sessions, once I click on a menu, the menu appears but then the entire desktop interface freezes.
I am not able to get it to respond any further except maybe if I Disconnect the session and then try to resume it. If I do, then the display might have progressed a little further toward what it should show (e.g. highlight the first menu entry) but the desktop is still unresponsive.
I checked the /var/log/syslog with debug logging level but didn't see anything helpful. I can post the output here or to something like Pastebin if desired.